The present invention relates in general to the field of image exposure devices and more particularly to an image exposure device having improved thermal compensation for a one-dimensional or two-dimensional array of light emitting elements.
Multiple channel image exposure devices having multiple light emitting elements have been used in imaging equipment to expose images on photosensitive media. One such device is described in U.S. Pat. No. 6,034,712, which uses an array of light emitting light elements disposed within recesses formed in a substrate and having a pinhole mask to expose an image on photosensitive media.
The photosensitive media may be of the type having a plurality of microcapsules with an image-forming material encapsulated within the microcapsules. To form an image on a photosensitive media of the type having microcapsules, a multiple channel image exposure device exposes desired microcapsules with at least one of the multiple light emitting elements. Exposure hardens desired microcapsules to a point such that when processed through a microcapsule rupturing device that utilizes pressure, the exposed microcapsules remain intact while the unexposed microcapsules are ruptured, releasing the encapsulated image-forming material to form an image within the photosensitive material. Similar imaging forming equipment is described in U.S. Pat. Nos. 4,440,846 and 4,339,209.
Multiple channel image exposure devices require accurate alignment. Depending on the application and or image resolution, the alignment accuracy may be required to be within a few microns to prevent image artifacts from being generated in an image formed on the photosensitive media due to misalignment of the multiple channel image exposure device. This becomes increasingly important at higher image resolution, and is difficult over a temperature range the device is required to operate at.
Thus, there is a need for improved thermal stability of an array of one-dimensional or two-dimensional multiple light emitting elements of a multiple channel image exposure device to provide longer life of the device, maintain alignment, and improved stability of the output of the light emitting elements.
Briefly, according to one aspect of the present invention an imaging apparatus for exposing a photosensitive material comprises a lenslet array; an array of light emitting elements in registration with the lenslet array; a printed circuit board having an array of thermal via wherein each of the thermal via is in contact with each of the light emitting elements; a thermal load plate; a thermal electric cooler connected to the thermal load plate; and a heat sink connected to the thermal electric cooler. The thermal load plate is bonded to the printed circuit board with a thermally conductive electrically isolating epoxy.
The present invention is intended to improve the performance of an imaging apparatus that uses a multiple channel imaging device to generate an image on or within a photosensitive media, preferably, but not limited to, a photosensitive media having a plurality of microcapsules, with an image-forming material encapsulated within the microcapsules. When exposed by a multiple channel image exposure device, desired microcapsules become hardened to a point that when processed through a microcapsule rupturing device, unexposed microcapsules are ruptured and release the image-forming material encapsulated within the microcapsules to form an image on or within the photosensitive media. The exposed microcapsules are not ruptured.
The multiple channel image exposure device of the present invention utilizes a molded lenslet array aligned to an array of one-dimensional or two-dimensional multiple light emitting elements to form a multiple channel image exposure device. To improve the output efficiency, increase life, and maintain the alignment of a multiple channel image exposure device, a printed circuit board is used having at least one thermal via to transfer the thermal load from the light emitting elements mounted on one side of the printed circuit board, to a thermal transfer pad on the opposite side of the printed circuit board, to a heat sink. A thermally conductive but electrically isolating epoxy is used between the printed circuit board and the heat sink to allow thermal transfer to, occur, but electrically isolating the printed circuit board from the heat sink. A thermal electric cooler is used to control the thermal transfer from, and to maintain the desired temperature of the light emitting elements. The intent is to maintain alignment of the light emitting elements during operational temperature changes, and to extend the life and maintain control of the output of the light emitting elements.
The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below.